Light and sun position calculator



Nov. 28, 1950 D. R. E. BROWN 2,531,932

LIGHT AND `SUN POSITION CALCULATOR Filed NOV. 23. 1949 ATTORNEY Nov. 28, 1950 D. R. E. BROWN 2,531,932

LIGHT AND SUN POSITION CALCULATOR Filed Nov. 23. 1949 3 Sheets-Sheet 2 ILLUMINATION IN FOOT CANDLES SOLAR ALTITUDE ATTORNEY Nov. 28, 1950 D. R. E. BROWN 2,531,932

LIGHT AND SUN POSITION CALCULATOR Filed Nov. 23, 1949 K lrTJEI- .'5 Sheets-Sheet 3 INVENTOR lDAYTON R. E. BROWN ATTURNEYS Patented Nov. 28, 1950 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 3 Claims.

The present invention relates to natural light and sun position calculators.

In planning military or naval operations it is often of great importance to know in advance what general illumination will obtain on a given date at a given time and place. Natural illumination has a direct influence on the visibility of objects of military and naval signiiicance. Also the design and construction of manufacturing plants, oilce buildings, homes and gardens can benefit from a study of the direction of the suns rays from hour to hour throughout the year.

Many persons concerned with natural light have found it troublesome to obtain nautical almanacs and sets of tables from which the suns position can be computed. Moreover, solving the astronomical triangle to ind the suns position is diiiicult to all but a limited few.

An important object of the present invention is to provide an instrument for use in estimating the amount of natural light present at any time, date and place.

Another object of the invention is the provision of an instrument foruse in finding the altitude or depression of the sun at any time, date and place.

A further object is to provide an instrument for use in finding the azimuth of the sun at any time, date and place.

The invention also aims to provide an instrument for use in nding the altitude and azimuth of stars whose declinations lie between 23.5 South and 23.5 North.

A further object is the provision of an instrument for use in iinding the time of sunrise and sunset at any date and place.

A still further object is to provide an instrument for assisting students of navigational astronomy in Visualizing the course of the sun and stars.

Other objects and many of the attendant advantages of this invention will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a top plan view of the computer,

Figure 2 is a vertical cross-sectional view substantially on the line 2-2 of Figure l,

Figure 3 is a graph of natural illumination as a function of solar altitude,

Figures 4 and 5 are diagrammatic views illustrating diurnal paths at 39 North Latitude,

Figures 6 and 7 are diagrammatic views illustrating diurnal paths at 90 North Latitude,

Figure 8 is a fragmentary diagrammatic view illustrating the use of the computer in finding the azimuth.

Figure 9 is an exploded perspective View of the computer.

Recently it was discovered that the entire range of light Values reaching the Earth from the sun and sky is only slightly affected by the weather but instead depends almost entirely on the altitude of the sun. This is true not only on clear days and moonless nights but also on average cloudy days and cloudy moonless nights. Thousands of observations were made in Widely separated places including the Arctic, the Antarctic, both temperate zones and the Tropics. From measurements obtained, the two curves shown in Figure 3 were constructed giving the values of light for all degrees of altitude and depression of the sun.

The curve shown by continuous line is for clear weather, that shown by dotted line is for average cloudy weather. These curves show that on average clear days a variation in altitude of the sun from the nadir, to the zenith, +90", changes the illumination from 0.00003 to 11,500 foot candles, a variation of nearly 4,000,000 percent, whereas the difference in illumination between clear and cloudy weather averages only about 30 percent and seldom reaches 80 percent under extreme conditions of dense cloudiness.

In the drawings which for the purpose of illustration show only a preferred embodiment of the invention, and wherein similar reference characters denote corresponding parts throughout the views, I0 generally designates the computer. As shown in Figures l and 2, the computer comprises a rectangular base plate il having an upper straight edge U30 parallel to horizon line I3! and circularly recessed to receive a lower rotary disc l2. A like lower straight edge I4! may b-e provided if desired. Coaxially of the circular recess the base plate l i is provided with an annular recess lS receiving an upper rotary transparent disc I4 held by ears 133 and ISA or other suitable means over the disc l2. Disc i 2 is operated through apertures |30 in disc i4. Disc i4 is provided with horizon line 32 normal to radius R as shown in Figures l and 9.

The annular surface dening the base of the recess i5 carries outer and intermediate semicircular scales A, B concentric with an inner circular scale C graduated in degrees. Extending diametrically of the degrees scale C is a North- South axis N-S, shown at 13|, and marking the horizon at any given place. This axis N-S is indicated at one end by the letter N near the left margin of the computer adjacent the mark of the scale C and at its opposite end by the letter S on the right margin adjacent the 180 mark. Slidable over the base plate II is a T-square I5 having a..tr-ansparent.blade I'icarryingV a 90 to +90 vertical altitude scalefIT:v which is a projection of the 0-180 degree divisions of scale C on a line normal to the North-South axis N-S;

The scale E? is therefore sinusoidally graduatedv The head of the T-square may be provided with plate.

The values of illumination in foot-candles.for

cloudy and clear Weather given in Figure 3 are plotted on the semi-circular scales A, B alongside the degrees scale Cirom 270- to 90as functions of solar altitude; Hence, when the altitude is known, a: corresponding average light value for` overcast: days` and nightsv and during rain, snow or fog may be read oif scale A and for clear, sunny days and clear, moonless, starry nights off scale B whether the sun is above or below'the horizon.

Suitable directions for use of the light com'- puters-andsun position calculator, and a chart I9=showing` theEquation of Time-are preferably appliedsto` thebase--plate- II as by printing: The Equation ofTime chartis'usedV in determining the true sun time (local apparent time) on any particular.r day whenthe mean sun time (local means solar time) is-known.

Delineated.l on the rotor disc I 2 and visible throught-he transparentdisc I4 lsadiurnal grid ZIJ comprising a. series off parallel lines, 2k3! and: crossing ares.l 3,2-58. The:- spaces between these parallel lines and crossing arcs may be-subdivided'by additional linesfsuch asl those shown butcnot. numbered inthe drawingsl The apparent` course ofthe sunl along itsdaily circuit around'. the Earth is-.veryv close` to a true circle and is called aidiurnal. The suns average rate ofi travel alonga diurnalpath is degrees per@ hour sol thatinZfhoursit completes a whole QircuitLof; 360. The computerv isdesigned toillustrate .graphicallyY the course of the suns Vtravel ona` diurnal relativey to the horizon,V thereby enablrlg the user tondthefaltitude of the sun atranytime of Iday or. night .at any selected place on; theeEarthssurface.y Inasmuch'as the North- Southaxis N-S represents the horizonWest .is considered to bel in front.- of; thecomputer and East behimipiit.

The selected geographicalv location is represented by the center Su-of-thefrotarydisc- I2.'- To aniobserver somewherel in ther United States the sun appears. torsefinthemorning above the horizon, as representedv byftheline N-Si in Figurefl, swing aroundthe sky and-gobelow the horizon again atsunset; In order to make solutions. possible/omthe computer, the-circular diurnalsareesimplied byfshowing-them as side View. projections forming the series of parallel lines` 2 I-3 I depicted Vin-Figure 5,:

The diurnal-g-ridZIl-may bel set forany given Ylatitude by aligning its arrow- 59,1-with the proper latitudeindi'cia onthedegreesscale C. Ifthe diurnalgridisset-for90 North Latitude as shown in; Figure 7, the topfdiurnaljlineZirepresents theapparent pathoftlfiesu-nV at the Northf'Pole onJune, 2*,1.Y ''heourved'lines 32-58f-shownin Eiguregl crossing the diurnalggrid Vd ividerthe':dil-

urnals ZI-Sl into time intervals. Instead of referring to hours as l-12 a. m. and p. m., the convention of numbering al1 24 hours consecutively is followed. Preferably the computer is made of a size to permit subdivision of the hours into smaller intervals. On June 21 the day starts atzmidnightandwthe sunsy positionlisgthen representedbyA a. point at the leftend ofil the top diurnal line. In the morning the suns hourly progress along its path is marked by the upper figures 1, 2 3, etc, till noon which is represented by-a point at the right end of the diurnal line. I ts afternoon progress is marked by the figures 13, 14, 15, etc. Actually then, to a personat' theNorth-Pole on June 21 the sun would appeary to describe a horizontal circle in the sky 23.5 above the horizon, as illustrated in Figuro.6.

Oni each: successive day the path is a trifle nearer the horizon inasmuch as the sun travels slowlydownward in! a continuous` spiral: until about September 23 when-it begins todisappea belowv they horizon. This progression fronnday today canbe followed-on a dotcalendar SI which inthepresent embodiment. of the invention is delineated on thetop transparent disc ifi.` Obviously the dot calendar: could be delineated di.- rectly onthediurnal gridflif desired. rIhis dot calendarS-if is used in selecting the proper diurnal.- or for--indingI the approximate declination ofthe sun. for. any'particular.y day of. the year. V/'henzthe arrow 59 of the diurnaldisc I2 andi an arrow 2`on the'top disc I4I are aligned, thefdotg of the calendar 6l mark the positions of. thediurnallineson the 1st, 6th; 11th, 16th. 21st,,and26th of eachmonth. About Decemf ber 2'1I thesun.reaches itslowestpointbelow the horizon and then gradually spirals 11p-again.

Thediurnalsare practicallyI- horizontal at .the SouthBole as Well asat the NorthPole, but to anobserver atL the Equator. the apparent path of the sun is up and down along a. semicircular archilflfaverticalv plane'.` For every degree that an, place-a is distant` from the.. Equator, the. plane ofeachdiurnal `slopes Y one degree ,-away from Y the vertical. The arrow- 59 whenpointed'tofa selecteddegree number. above the.North:-South axis automatically sets all of the diurnalsA for, the NOrtmLatitudeOf that number. Figure-.V5 shows thediurnalgrid set for the, latitude-of Wash,- ington,.D. C., which isv approximately-39 North. To set the diurnals for 39 South` Latitude, it isnecessary topointr the arrow 39 below the horizon line; NeSto theplace onA the. scaleC marked 321.

Inl the Northern Hemisphere the sun-on any givendate is farthest SouthatNoon andffarthesi, North` at, Midnight, whereas in the Southern Hemisphere the sun is farthest South at Mid,- nightandfarthest North at .Noem At .the North and. South Roles the progression of the.. diurnals over a years timeis up and down, whereas at the Equator the progression is lateralin ,aNorth andSouth direction. Elsewhere the` Vprogression ofthe' diurnalsV over a years time is somewhat North and South, thatis; thediurnalfor June 21 is farthest to the North, for December121 farthest to the-South;

Delineated onr the -upper transparentY disc'v I4 is arrV altitude circle scale 63 for usein nding the suns azimuth. Itznisf atprojection'r offrthe UFL-quadrant oflscale Cl on a rotatableradius R aligningr with the arrow 62. Unlike scale` H however, the graduations OffthealtitudecircIe scale;V 631A projectedf from the y 0"'-902v quadrantI of scale C are reversely marked 90-0 respectively. Scale 63 is therefore cosinusoidally graduated. These mark the radii of altitude circles projected on the N-S horizon.

AThe steps for nding the solar altitude are briey as follows:

First, the lower and upper discs I2, I4 are rotated until the arrows 59, 62 point to a mark on the degrees scale C corresponding to the latitude of a given place for which the solar altitude is desired.

Second, from the diurnal lines 2I-3I on the lower disc I 2 one line is selected which appears to intersect the dot marking the date on the upper transparent disc I4.

Third, the position of the sun along its diurnal path at the given time is found by locating the point of intersection of the proper one of the time lines 32-58 with the previously selected diurnal line.

Fourth, the altitude of the suns position above the horizon is found by reference to the vertical altitude scale I'! which measures the angular distance between the axis N-S representing the horizon, and the previously located intersection point representing the suns position.

Corrections for Longitude and for differences between clock time, Imean solar time and true solar time are made in the usual way.

The following problems illustrate the operation of the device:

PROBLEM 1 Find the altitude of the sun and the amount of natural illuminaton on a clear day at Washington, D. C., at :00 Eastern Standard Time on the 16th of August. Washington, D. C.=Lati tude 39 North, Longitude '77 West.

Rough solution 1. Set both disc arrows 59, 62, to 39 on scale C, as shown in Figure l.

2. Find 10:00 Eastern Standard Time on the diurnal for August 16.

Noria-The diurnal for August 16 starts at the mark 323 on scale C, passes directly under the dot for August 16, and reaches the mark 115 on scale C at Noon. The suns position at 10:00 is where the 10th hour curve 10-10 crosses the diurnal for August 16.

3. Measure the altitude for 10:00 with the T-square altitude scale I1.

Answer Altitude :53 1/2 Illumination=8500 foot-candles. This quantity is read oiT scale B adjacent the 531/2o mark on scale C.

In the foregoing rough solution, Eastern Standard Time was used. The Mean Solar Time at any given instant at a given place differs from Zone Standard Time by an amount directly proportional to the distance that that place is Eastward or Westward from the Zone Meridian. For each degree of Longitude a place is East of the Zone Meridian the Mean Solar Time is 4 minutes faster than the clock. For each degree a place is West of the Zone Meridian the Mean Solar Time is 4 minutes slower than the clock. For a more accurate solution, a correction of time for longitude is therefore necessary.

Mean Solar Time is measured by the regular motion of an imaginary sun since the motion of the real sun is not regular. The real sun gets behind and again ahead of its average schedule by as much as 16 minutes. This diierence is shown in the Equation of Time chart. A more accurate solution therefore requires a correction for the difference between Mean Solar Time and True Solar Time.

Problem 1.-More accurate solution 1. Correct Eastern Standard Time to Mean Solar Time at Washington, D. C.

77 West=Longitude of Washington, D. C.

75 West=Longitude of Eastern Standard Time Zone Meridian 2 West=DiiTerence 4 minutes=Time clierence per degree 8 minutes=Correction 10:00=Eastern Standard Time -1 08=Correction 09:52=Mean Solar Time at Washington, D. C.

2. Correct Mean Solar Time lto True Solar Time for August 16.

09 z 52=Mean Solar Time `104.3:Equation of Time correction for August 09:47.7:True Solar Time 3. Set the arrows 59, S2 oi both discs to 39 on scale C.

4. Select the diurnal for August 16 and locate the suns position for 09:47.? on the diurnal.

5. Measure the solar altitude with the T- square altitude scale I'I.

i Answer Altitude: 51 1/2 Illumination=8l75 foot-candles.

PROBLEM 2 Find the azimuth oi the sun at 10:00 Eastern Standard Time on August 16 at Washington, D. C.

Solution Azimuth is the angular distance around the Horizon from some starting point, generally North. The Azimuth is measured in degrees generally starting with North as 0 and going in the direction North, East, South, West. This is the convention used in the U. S. Navy.

1. Find the suns position on the diurnal line as in the latter solution of Problem 1. This is point SP in Figure 8.

2. Set the center line of the T-square scale I'I directly over this sun position and secure the T-square in place, as by clamping screw I 8, as

3. Make a note of the solar altitude as 511/2o and then rotate the diurnal grid disc I2 to enable an easier reading if the grid indicia interferes.

4. Rotate the transparent upper disc I 4 until the center of the 51 1/2 mark on the altitude circle scale 63 crosses the vertical center line of the T-square scale i?. This center is point CTR in Figure 8.

5. Read the Azimuth on scale C under the top disc arrow head 6.2 below the word Azimuth Answer=122.

Nora-The foregoing explanation permits one of two answers for Azimuth, one occurring before and one after noon for the same setting of the vertical T-square scale 17. Care should be taken, especially for the Tropics and for South Latitudes also to note which is the logical answer.

PROBLEM 3 Find the Eastern Standard Time of Sunrise and Sunset for August 16 at Washington, D. C.

, Solution '1;"Set, the uppervand'jlower disc arrows A59, f 62 to39 as in Problems 1 and 2. l

2. Slide the T-square blade`|6 loverf'to'where the linefma-rked Sunrise'funset crossesthe di- ...urnal for AugustV 16.

3. Read on the diurnal:

Sunrise= :.09 MeanjSolar Time Y. Sunset=e18 51. Mean `s olarlfime 4. Convert Mean Solar Time tofEastern'Standard Time and also correct for thel Longitude of Washington; 135C.

Various modications may be made in theform of invention herein shown. anddescribed Without ,.departingfromthe spirit of theinvention orY the scope oi the following claims.

Theinvention described` hereinl maybe manufactured-.andused by or for the Government of the United States of Americafor vgovernmental purposes without the payment. ofaanygroyalties thereon or therefor.

I claim:

1. A computer, comprising: -a flat base; a lower circular recess inthe -upper-surface ofsaid base having a first diameter :aconcentric upper recess in said surface having `a greaterdiametema flat Yannui'ar-banal intermediate the circumferencesof said recesses; a horizontal diameter line across the center of said band; l,a horizontal straight edge at the top of said surface; a T-square member V:slidable onsaid. edge. and having on vits-blade `atransparentaltitude scalevertical to` said diamieter: said band having thereon aclear-skylight .fsca1e, an overcast-.sky light scales-and -aciroular ',-latitude scale; a lower disc rotatable infsaid lower recess and having a .diurnal grid thereon, -said grid having a vertical transverse axis; an upper transparent disc 'rotatable in said upper r-recess land f having ;marked thereon a diameter andra radius vertical to said diameter; sa-idradiushaving .an altitude circlefvalue :scalethereon; 1 said z upper 'disc having Avapertures therein for manually rotating said llower member therethrough; said upper member having daterscalesthereon` positionedf to overlie said grid, whereby said-members may be selectively positioned' to v vdetermine the altitudeand azimuth of :the sun and thefnatural illumination on any given place atfanytime.

"2. Acomputercomprising a base; .a dat-annular surface; a lower-"disc rotatable in-registra- `tion with the inner periphery of said-annular surface; a transparent upper disc rotatable concentrically'with said lower disc and dimensioned to overlie said surface .and said lower disc; a horizontal diameter line across said surface; said base having 4a vhorizontal straight edge; na T,square :member 'having its headfslidableion said edge-and having a transparent V altitude scale roniitsffblade -f-verticalitosaid horizontal line; .latitude fandillumination scales on said surface; v a diurnalggrid con said) lower disc; said grid having-.aitransverse axis line vertical to said grid; a diameter 'line'on fesaid upper disc anda radius line normal thereto;

.1 an altitude .circlevalue scale' on said radius; date escales on said upper disc positioned to overlie said sgrid, whereby said discs may be rotated-zandfsaid blade positioned thereover to positions fromzwhioh :thesaltitude and azimuth oifthe sun zandthe v:natural illumination on any given place fat any ttime may be readv from said positions.

3. In a computer; a flat base; .a oircular"360 jj latitude scaleV thereon having `a Ozto 180 axis line @representing-the,horizon; an adjacent scale'for rclear:y sky `illumination and an Aadjacent scale for overcast-.sky illumination concentric :with `-and graduated in relation to said latitude scaleyeach fof Vsaid illumination scales extending above'and below said horizon line; a iirst rotatable discfadjacentto and concentric-.with said latitudev scale; V'said vfirst disc having a horizontal diurnal grid fconcentric with vsaid latitude scale; said grid having thereon a vertical transverse axis liney and arcuate lines indicating'hour graduations; a sec- `-ond .transparent disc concentric withandoverlying said scalesl and said rst disc; saidsecond :disc-having markedthereon a center point-representing the operators location anda diameter and a radius verticalztosaid diameter; said radius having thereon an altitude circlescale Agraduated in relation to said latitude scale; a date scale on said second disc graduated. in relation to said grid anfgpositioned to overlie said grid; a transparent scale vertical tosaid horizoniline. and arranged for slidable movement horizontal to said horizon line; said slidablesscale having at its midpoint a sunrise and sunset line adapted tobe .coincident with said horizon line; saidslidable,transparent vertical scale being graduatedlabove said horizon `line in0 to +90 and below lsaid horizon. linenin 0 to 90 in relationship to said latitude scale, whereby the illumination naturally falling upon any pla-ce at any timeof day or night may be determined by selectively positioning said discsy and said slidable scale.

DAYTON R. E. BROWN.

REFERENCES CITED The following references are of record in the iile of this patent:

` UNITED STATES PATENTS Number Name Date 780,178 Henning Jan. 17, 1905 v910,230 Pratt Jan. 19,1909 `'990,764 Morse Apr.' 25, 1911 1,742,781 Ott Jan. 7,1930 2,495,777 Schroeder Jan: 31,1950

FOREGN PA-TENTS iNumoer Country 'Date 156,033 GreatBritain J an.'6, 1921 

